Rootstock Interaction with Cultural Practices
This report contains the results of three studies centered on the question of how rootstocks may interact with cultural practices. Because of limited space, this summary will focus on the results of a) how rootstock performance differs in response to crop load and b) how rootstocks respond to in-row spacing under dry-farmed conditions. In the first study, beginning in 1995, Cabernet Sauvignon grown on four rootstocks (3309, 5C, 110R, and 039-16) were balance pruned to four different pruning formulae (5, 7.5, 10, and 12.5 buds/lb of 1- and 2-year-old wood). In the third year of study, the vines have begun to attain a stable partitioning of crop and vegetative growth. The rootstock influenced rate of maturation. Vines on 3309 had the highest average soluble solids at harvest followed by 110R, 039-16, and 5C (24.6, 23.7, 23.5, and 23.3 °Brix respectively). Higher pruning formulas delayed maturity both directly and through influences on crop load. While still significant, differences in maturation were minimized by rootstock dependent cropping patterns and increased by pruning formula effects on crop. Vines on 039-16 produced lower yields than those on other rootstocks; 6.2, 7.5, 8.5, and 8.5 kg/vine for 039-16, 3309, 5C, and 110R, resp. Pruning formula affected all components of yield except berry weight. The increase in buds retained at each higher formulas resulted in more shoots and more clusters per vine. The net effect was a 30%increase in crop from the 5 to the 12.5 bud/lb treatment. Leaf area per gram crop decreased with increasing pruning formula from 13.8 to 8.2 cm2 / gm but did not vary by rootstock. In the second study, three putative rootstocks (11 OR, 1103P and 140Ru) were compared with a putative drought-sensitive rootstock (5C) at three in-row spacings (1.0, 1.6, and 2.2 m) to test whether, under non-irrigated conditions, rootstocks performed differently when increasing soil volumes were available. Shoot spacing was held constant at about 12 shoots/m cordon. In 1997 regardless of the vine spacing, 5C showed less growth per m cordon as a result of shorter shoots. 5C also had less yield per meter cordon, at the wider spacings, as a result of fewer clusters/m (despite equal shoots/m) and fewer berries/cluster. Vines at the 1.0 m spacing ripened before the wider spacings and 5C at all spacings ripened first. Water status measurements showed that 5C had among the highest values for water potential (least drought), although no vines showed less than -1.4 MPa. Investigations in 1998 will concentrate on whether 5C’s water status may be due to lower leaf area/vine than the more vigorous “drought-resistant” rootstocks.